Relative reactivities cyclic hydrocarbons

Although the Hiickel method has now been supplanted by more complete treatments for theoretical analysis of organic reactions, the pictures of the n orbitals of both linear and cyclic conjugated polyene systems that it provides are correct as to symmetry and the relative energy of the orbitals. In many reactions where the n system is the primary site of reactivity, these orbitals correctly describe the behavior of the systems. For that reason, the reader should develop a familiarity with the qualitative description of the n orbitals of typical linear polyenes and conjugated cyclic hydrocarbons. These orbitals will be the basis for further discussion in Chapters 9 and 11. 

Relative Reactivities of Cyclic Hydrocarbons with 4-7 Membered Rings" (78)... 

The relatively higher reactivity of the smaller cyclic hydrocarbons can be justified on the basis of their increased strain energy (Chapter 4). 

Addition of the strong CH bond of cyclopropane (106 Kcal/mole) is favoured over insertion into the relatively weak C—C bond this result rules out hydrogen abstraction reaction of radicals which favour CH bond with low bond energies. In fact, cyclopropane is the cyclic hydrocarbon with the highest reactivity towards CH insertion (Figure 1). 

The contribution of the various classes of hydrocarbons to the formation of particulate organic compounds is a complex function of their relative ambient concentrations, gas-phase reactivity, and ability to form products whose physical properties, especially vapor pressures, are of prime importance in the physical mechanisms controlling the gas-to-aerosol conversion process. In view of the results discussed previously, cyclic olefins appear to be the most important class of organic aerosol precursors. This is due to their high gas-phase reactivity and their ability... 

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